A) Field of the Invention
This invention relates to a solid state imaging device, especially to a structure of a solid state imaging device for a digital still camera.
B) Description of the Related Art
FIG. 10 is a schematic plan view of a conventional solid state imaging device 800.
The solid state imaging device 800 is the most commonly used interlace-type CCD (ITCCD) as a conventional solid state imaging device. A large number of photoelectric conversion elements (pixels) 812 are arranged in a tetragonal matrix in a light receiving region 802. A vertical electric charge transfer device (vertical charge coupled device: VCCD) 814 that reads out signal charges generated at the photoelectric conversion elements 812 and vertically transfers is formed including transfer electrodes and a vertical transfer channel for each column of the photoelectric conversion elements 812 and transfers the signal charges generated at photoelectric conversion elements 12 in a vertical direction.
In the drawing, a horizontal electric charge transfer device (horizontal charge coupled device: HCCD) 803 that transfers electric charges transferred by the VCCD 814 to a peripheral circuit 804 line by line is formed under the light receiving region 802. Also, pixel lines on lines indicated with white arrows are first field lines in an interlace scanning method, and pixel lines on lines indicated with black arrows are second field lines.
A color filter arrangement corresponding to each pixel is presented with letters “R, G and B” in each pixel. Here in this specification, R, G and B respectively indicate red, green and blue. The color filter arrangement adopted in this solid state imaging device 800 is so-called Bayer arrangement and generally used for the solid state imaging device as an imaging device for a digital still camera (DSC).
FIG. 11 is a schematic plan view of a conventional solid state imaging device 900.
The solid state imaging device 900 is composed including a light receiving region 902 including vertical electric charge transfer devices (VCCD) 914 that vertically transfer signal charges generated at a large number of photoelectric conversion elements 912 and the photoelectric conversion elements, a horizontal electric charge transfer device (HCCD) that horizontally transfers the signal charges transferred by the VCCDs 914 and an output amplifier 904.
The receiving light region 902 of the solid state imaging device to which Pixel Interleaved Array CCD (PIACCD) is adopted as shown in the drawing has a large number of pixels arranged in the pixel interleaved arrangement. In each interval of columns of photoelectric conversion elements 912, a vertical electric charge transfer device 914 that reads out the signal charges generated at the photoelectric conversion elements 912 and vertically transfers is provided with vertically winding a space between the columns of the photoelectric conversion elements 912. A transfer channel is positioned to the winding space formed by the pixel interleaved arrangement, and adjacent transfer channels are separated via the photoelectric conversion elements and come closer via the channel stop region 903 (for example, refer to JP-A Hei10-136391 (patent document 1) and Tetsuo Yamada and others, “A Progressive Scan CCD Imager for DSC Applications”, ISSCC Digest of Technical Papers, February, 2002, Page 110 (non-patent document 1)).
Each of the vertical electric charge transfer device 914 is formed including a vertical transfer channel (not shown in the drawing) and transfer electrodes formed to a horizontal direction over the vertical transfer channel via an insulating film (not shown in the drawing) winding a space between horizontally adjacent photoelectric conversion elements 912.
In the drawing, the color of the color filter (for example, green, blue or red) corresponding to each pixel is indicated by the letter G, B and R in each of the pixels 912. Also, pixel lines on lines indicated with white arrows are first field lines in the interlace scanning method, and pixel lines on lines indicated with blacks arrow are second field lines.
When the signals for the first field lines are read, the first G-line and the third G-line, and the fifth G-line and the seventh G-line are read. When the signals for the second field lines are read, the second G-line and the fourth G-line, the sixth G-line and the eighth G-line are read. As shown in the drawing, each G-line is formed along a solid line repeatedly connecting a center of each pixel.
FIG. 12A to FIG. 12D are diagrams showing signal arrangements read by the conventional ITCCD solid state imaging device 800.
FIG. 12A is a diagram showing a signal arrangement of the first field, and FIG. 12B is a diagram showing a signal arrangement of the second field. Both of the first field and the second field add same colored signals in every two lines. As a result, as shown in FIG. 12C, a signal arrangement of a vertical two-pixel addition field synthesized frame generated by synthesizing each field after the vertical addition can be obtained. Moreover, the conventional reading method for the ITCCD cannot reproduce a colored motion picture. Because each field includes only two types of signals such as G and R color signals or G and B color signals, one field cannot generate color signals including all of R, G, and B color signals. Since the color signal including R, G and B can be naturally generated after the field synthesis, the color signal after the synthesis, for example, can be used for a still picture with decreased number of pixels. In this case, sensitivity will be about twice by the addition of the signals.
FIG. 12D is a diagram showing spatial sampling centers after the vertical additions. The sampling points of G formed by the vertical addition of the first field with the Bayer Arrangement will be on lines indicated by white arrows, and the sampling points of G formed by the vertical addition of the second field with the Bayer Arrangement will be on lines indicated by black arrows. As obvious from the drawing, the sampling centers of the G signals after the vertical additions do not have regular intervals. Also, since the spatial sampling centers overlap with each another in wide areas, resolution obtained for the number of the sampling points will be lowered.
FIG. 13A to FIG. 13D are diagrams showing signal arrangements read by the conventional PIACCD solid state imaging device 900.
FIG. 13A is a diagram showing a signal arrangement of the first field, and FIG. 13B is a diagram showing a signal arrangement of the second field. In the first field, the first G-line and the third G-line are added, and the fifth G-line and the seventh G-line are added. In the second field, the second G-line and the fourth G-line are added, and the sixth G-line and the eighth G-line are added. As a result, as shown in FIG. 13C, a signal arrangement of a vertical two-pixel addition field synthesized frame generated by synthesizing each field after the vertical addition can be obtained. Moreover, it is different from the conventional reading method for the ITCCD because each field includes color signal for all colors of RGB. Therefore, the color signals of RGB can be generated in one field, and colored motion picture signals can be generated.
FIG. 13D is a diagram showing spatial sampling centers after the vertical additions. The sampling points of G obtained by the vertical addition of the first field with this conventional solid state imaging device 900 are on a line indicated by white arrow, and those by the vertical addition of the second field are on a line indicated by black arrow. That is, as same as the case of the conventional solid state imaging device 800 shown in FIG. 12D, the sampling centers of the G signals after the vertical additions do not have regular intervals. Also, since spatial sampling ranges of the adjoining sampling points are overlapped each another in a wide range, resolution obtained for the number of the sampling points will be lowered.
As described in the above, in the conventional vertical addition method, vertical resolution after the addition synthesis does not reach less than ½ of that before the addition synthesis and decreases about ¼. Therefore, although the sensitivity can be increased by the vertical addition in the interlace operation of the conventional vertical addition method, the vertical resolution may be lowered.